The present invention tackles the problem of the thermal conditioning of electronic components, and has been developed with particular regard to possible application to the temperature control of semiconductor laser modules.
In this field of application it is important to ensure the stability of the operating conditions. This is particularly true of wavelength division multiplexing (WDM) systems, and especially for high-density (DWDM) systems, where it is necessary to control the temperature of the laser accurately, since the emission frequency depends directly on the temperature of the component, with a coefficient of proportionality of the order of approximately xe2x88x9210 GHz/xc2x0C. Since rather small channel spacings, of the order of 50 GHz for example, are used in the most recent systems, it is necessary to ensure temperature stability in a range of values below 1xc2x0 C.
To achieve the necessary temperature stabilization, circuits have been developed which use a temperature-sensitive resistor (for example an NTC thermistor) as the sensor and a thermoelectric cell (Peltier cell) as the temperature control or conditioning element. These circuits can be used to stabilize the temperature of the sensor within a range of 0.5xc2x0 C. without any special circuit arrangements.
The control circuit regulates the current in the Peltier cell in such a way as to keep the sensor reading equal to a reference reading. However, since the position of the temperature sensor does not exactly coincide with that of the laser diode (referred to simply as the xe2x80x9claserxe2x80x9d in the following text), there may be a temperature difference between the laser and the sensor, which depends on the structure of the package containing the component. Consequently, the actual temperature of the laser can vary considerably, particularly with a change in external temperature, despite the correct operation of the temperature control. While the temperature of the sensor is kept constant by the control circuit, there may be, depending on the particular structure of the package, either conditions in which the actual temperature of the laser rises with an increase in the temperature of the package, or conditionsxe2x80x94most frequently encountered in commercial componentsxe2x80x94in which the temperature of the laser falls with an increase in the external temperature.
A situation of this type is shown schematically in FIG. 1 of the attached drawings, which shows three parallel vertical lines, each corresponding to an ideal temperature scale. Moving from left to right, we find three scales of possible temperature values, corresponding, respectively, to the package, the temperature sensor (thermistor) and the laser: thus it can be seen that, even if the temperature of the sensor is kept constant, the variations of temperature in the package cause corresponding variations of the temperature of the laser and therefore a variation of the operating conditions of the laser.
The paper by A. Adachi, S. Kaneko, J. Yamashita and K. Kasahara, xe2x80x9cLow-frequency drift laser-diode module for a wide temperature range using two thermistorsxe2x80x9d, published on pages 109 and 110 of the OFC/IOOC ""93 Technical Digest describes a solution (taken as the model for the preambles of claims 1 and 7) in which two thermistors, one located in proximity to the laser and the other at a certain distance from the first thermistor, are positioned on the base plate carrying the laser. The different temperatures read by the two thermistors are used to produce a kind of estimate or interpolation of the temperature difference present between the first thermistor and the laser.
Even without a discussion of the real effectiveness of a solution of this kind, it is immediately apparent that it necessarily entails the provision of the second thermistor during the manufacture of the package comprising the laser. This solution is therefore not applicable to commercial components, which are supplied already sealed into their packages, or, in other words, when it is no longer possible to modify the base plate of the component.
The object of the present invention is to overcome the aforesaid disadvantage with a solution which is also applicable to commercial components (and therefore to those already enclosed in their packages), without the need to make modifications inside the package, and which, in all cases, provides very precise temperature control.
According to the present invention, this object is achieved by means of a process having the characteristics claimed specifically in the following claims.
The invention also relates to the corresponding device.
Briefly, the solution according to the invention provides a control circuit which is designed to make the reading of the sensor equal to that of a reference made to vary as a function of the external temperature, measured by another sensor preferably located in contact with the package.
In general, the references madexe2x80x94both here and in the following claimsxe2x80x94to the temperature conditioning of electronic components are intended to allow for the fact that the possible range of application of the invention is not in any way restricted to the cooling of a laser module by means of Peltier cells, although reference has been and will be made to this application by way of example.
In particular, the solution according to the invention is suitable for use for a thermal conditioning (temperature control) operation intended for cooling a component which tends to heat up during operation and/or to heat a component whose temperaturexe2x80x94for a wide range of reasonsxe2x80x94is to be raised (for example, in order to obtain a fixed operating temperature even in the presence of a lower external temperature). Clearly, however, it is possible that, in many case, the same component may be concerned, being intended to be alternatively cooled and heated in the presence of different environmental and/or operating conditions. The means of thermally conditioning the component (shown schematically here in the form of a Peltier cell, intended primarily to cool the component) can therefore be produced and/or controlled (according to entirely known principles) in such a way that the component can be heated, in addition or as an alternative to the cooling.
This component can consist of a component of any kind or nature.
The invention will now be described, purely by way of example and without restrictive intent, with reference to the attached drawings in which: